So far, stroke genetics has the reputation of daunting complexity and heterogeneity. However, progress through efforts at studying the human genome has provided novel technologies and focus, and 12 stroke genes or loci have already been identified in the last years, usually through the study of large pedigrees. However, particularly little is known about the ischemic form of stroke, and only recently could one chromosomal locus be shown to exert a major effect on stroke latency and outcome - through QTL studies in mouse strains. Whether the outstanding role of this one gene locus is also true in humans should be tested in linkage analyses of large pedigrees. The characterization of such families will probably be essential for progress in molecular genetics of ischemic stroke as well as being a challenge for clinical stroke centers.